Biology

Fuente:https://en.wikipedia.org/wiki/Biology
Biology is a natural science concerned with the study of life and living organisms, including their
structure,function,growth,evolution,distribution,andtaxonomy.[1] Modernbiologyisavast and
eclecticfield,composedof manybranchesand subdisciplines.However,despitethe broadscope of
biology,thereare certaingeneralandunifyingconceptswithinitthatgovernall studyandresearch,
consolidatingitintosingle,coherentfields.Ingeneral,biologyrecognizesthe cell as the basic unit
of life, genes as the basic unit of heredity, and evolution as the engine that propelsthe synthesis
andcreationof newspecies.Itisalsounderstoodtodaythatallorganismssurvive byconsumingand
transforming energy and by regulating their internal environment to maintain a stable and vital
condition.
Subdisciplines of biology are defined by the scale at which organisms are studied, the kinds of
organisms studied, and the methods used to study them: biochemistry examinesthe rudimentary
chemistry of life; molecular biology studies the complex interactions among biological molecules;
botanystudiesthe biologyof plants;cellularbiologyexaminesthe basicbuilding-blockof all life,the
cell;physiologyexaminesthe physical andchemical functionsof tissues,organs,andorgansystems
of an organism;evolutionarybiologyexaminesthe processesthatproducedthe diversityof life;and
ecology examines how organisms interact in their environment.
History
Main article: History of biology
A Diagram of a fly from Robert Hooke's innovative Micrographia, 1665
Ernst Haeckel's Tree of Life (1879)
The termbiologyisderivedfromthe Greekwordβίος,bios,"life"andthe suffix -λογία, -logia,"study
of."[3][4] The Latin form of the term first appeared in 1736 when Swedish scientist Carl Linnaeus
(Carl vonLinné) usedbiologi inhisBibliothecabotanica.Itwasusedagainin1766 in a workentitled
Philosophiae naturalis sive physicae: tomus III, continens geologian, biologian, phytologian
generalis,byMichael ChristophHanov,adiscipleof ChristianWolff.The firstGermanuse,Biologie,
wasin a 1771 translationof Linnaeus'work.In1797, TheodorGeorgAugustRoose usedthe termin
a book, Grundzüge der Lehre van der Lebenskraft,in the preface. Karl Friedrich Burdach used the
term in 1800 in a more restricted sense of the study of human beings from a morphological,
physiological and psychological perspective (Propädeutik zum Studien der gesammten Heilkunst).
The term came into its modern usage with the six-volume treatise Biologie, oder Philosophie der
lebenden Natur (1802–22) by Gottfried Reinhold Treviranus, who announced:[5]
The objectsof ourresearchwill be the differentformsandmanifestationsof life,the conditionsand
lawsunderwhichthese phenomenaoccur,andthe causesthroughwhichtheyhave beeneffected.

The science that concerns itself with these objects we will indicate by the name biology [Biologie]
or the doctrine of life [Lebenslehre].
Althoughmodernbiologyisarelativelyrecentdevelopment,sciencesrelatedtoandincludedwithin
it have been studied since ancient times. Natural philosophy was studied as early as the ancient
civilizations of Mesopotamia, Egypt, the Indian subcontinent, and China. However, the origins of
modern biology and its approach to the study of nature are most often traced back to ancient
Greece.[6][7] While the formal studyof medicine datesback to Hippocrates (ca. 460 BC – ca. 370
BC), it was Aristotle (384 BC – 322 BC) who contributed most extensively to the development of
biology.Especiallyimportantare hisHistoryof Animalsandotherworkswhere heshowednaturalist
leanings, and later more empirical works that focused on biological causation and the diversityof
life. Aristotle's successor at the Lyceum, Theophrastus, wrote a series of books on botany that
survivedasthe mostimportantcontributionof antiquitytothe plantsciences,evenintotheMiddle
Ages.[8]
Scholars of the medieval Islamic world who wrote on biology included al-Jahiz (781–869), Al-
Dīnawarī (828–896), who wrote on botany,[9] and Rhazes (865–925) who wrote on anatomy and
physiology.Medicine was especially well studiedby Islamic scholars working in Greekphilosopher
traditions,whilenatural historydrewheavilyonAristotelianthought,especiallyinupholdingafixed
hierarchy of life.
Biologybeganto quicklydevelopandgrow withAnton van Leeuwenhoek'sdramaticimprovement
of the microscope. It was then that scholars discovered spermatozoa, bacteria, infusoria and the
diversityof microscopiclife.InvestigationsbyJanSwammerdamledtonew interestinentomology
and helped to develop the basic techniques of microscopic dissection and staining.[10]
Advancesinmicroscopyalsohadaprofoundimpactonbiologicalthinking.In the early19thcentury,
a number of biologists pointedto the central importance of the cell. Then,in 1838, Schleiden and
Schwann began promoting the now universal ideas that (1) the basic unit of organisms is the cell
and (2) that individual cellshave all the characteristicsof life,althoughtheyopposedthe ideathat
(3) all cells come from the divisionof other cells. Thanks to the work of Robert Remak and Rudolf
Virchow,however,bythe 1860smostbiologistsacceptedall threetenetsof whatcame to be known
as cell theory.[11][12]
Meanwhile, taxonomy and classification became the focus of natural historians. Carl Linnaeus
publishedabasictaxonomyforthe natural worldin1735 (variationsof whichhavebeeninuse ever
since), and in the 1750s introduced scientific names for all his species.[13] Georges-Louis Leclerc,
Comte de Buffon, treated species as artificial categories and living forms as malleable—even
suggestingthe possibilityof commondescent.Thoughhe wasopposedtoevolution,Buffonis akey

figure inthe historyof evolutionarythought;hisworkinfluencedthe evolutionarytheoriesof both
Lamarck and Darwin.[14]
Seriousevolutionarythinkingoriginatedwiththe worksof Jean-Baptiste Lamarck,whowasthe first
to present a coherent theory of evolution.[15] He posited that evolution was the result of
environmental stressonpropertiesof animals,meaningthatthe more frequentlyandrigorouslyan
organ was used, the more complex and efficientit would become,thus adapting the animal to its
environment.Lamarckbelievedthatthese acquiredtraits could thenbe passedon to the animal's
offspring, who would further develop and perfect them.[16] However,it was the British naturalist
CharlesDarwin,combiningthe biogeographical approach of Humboldt,the uniformitariangeology
of Lyell, Malthus's writings on population growth, and his own morphological expertise and
extensive natural observations,whoforgedamore successful evolutionarytheorybasedonnatural
selection;similarreasoningandevidenceledAlfredRussel Wallacetoindependentlyreachthesame
conclusions.[17][18] Although it was the subject of controversy (which continues to this day),
Darwin'stheoryquicklyspreadthroughthe scientificcommunityandsoonbecame acentral axiom
of the rapidly developing science of biology.
The discovery of the physical representation of heredity came along with evolutionary principles
and population genetics. In the 1940s and early 1950s, experiments pointed to DNA as the
componentof chromosomesthat heldthe trait-carryingunitsthat had become knownas genes.A
focusonnewkindsof model organismssuchasvirusesandbacteria,alongwiththe discoveryof the
double helical structure of DNA in 1953, marked the transition to the era of molecular genetics.
From the 1950s to present times,biology has been vastly extendedin the molecular domain.The
geneticcode wascrackedbyHarGobindKhorana,RobertW.HolleyandMarshall WarrenNirenberg
afterDNA was understoodtocontaincodons.Finally,the HumanGenome Projectwaslaunchedin
1990 withthe goal of mappingthe general humangenome.Thisprojectwasessentiallycompleted
in 2003,[19] with further analysis still being published. The Human Genome Project was the first
step in a globalized effort to incorporate accumulated knowledge of biology into a functional,
molecular definition of the human body and the bodies of other organisms.
Foundations of modern biology
Cell theory
Human cancer cells with nuclei (specifically the DNA) stained blue. The central and rightmost cell
are in interphase,sothe entire nuclei are labeled.The cell onthe leftis goingthrough mitosisand
its DNA has condensed.
Main article: Cell theory

Cell theorystatesthatthe cell isthe fundamentalunitof life,andthatall livingthingsare composed
of one or more cellsorthe secretedproductsof those cells(e.g.shells,hairsandnailsetc.).All cells
arise from other cells through cell division. In multicellular organisms, every cell in the organism's
body derives ultimately from a single cell in a fertilized egg. The cell is also considered to be the
basic unitin many pathological processes.[20] Inaddition,the phenomenonof energyflow occurs
in cells in processes that are part of the function known as metabolism. Finally, cells contain
hereditary information (DNA), which is passed from cell to cell during cell division.
Evolution
Natural selection of a population for dark coloration.
Main article: Evolution
A central organizingconceptinbiologyisthatlife changesanddevelopsthroughevolution,andthat
all life-formsknownhaveacommonorigin.The theoryof evolutionpostulatesthatall organismson
the Earth, both living and extinct, have descendedfrom a common ancestor or an ancestral gene
pool.This last universal commonancestorof all organismsis believedtohave appearedabout 3.5
billionyearsago.[21] Biologistsgenerallyregardthe universalityandubiquityof the geneticcode as
definitiveevidence infavorof the theoryof universal commondescentforall bacteria,archaea,and
eukaryotes (see: origin of life).[22]
Introduced into the scientific lexicon by Jean-Baptiste de Lamarck in 1809,[23] evolution was
established by Charles Darwin fifty years later as a viable scientific model when he articulated its
drivingforce:natural selection.[24][25][26] (AlfredRusselWallace isrecognizedasthe co-discoverer
of thisconceptas he helpedresearchandexperimentwiththe conceptof evolution.)[27] Evolution
is now used to explain the great variations of life found on Earth.
Darwintheorizedthatspeciesandbreedsdevelopedthroughthe processesof natural selectionand
artificial selectionorselective breeding.[28] Geneticdriftwasembracedasanadditionalmechanism
of evolutionary development in the modern synthesis of the theory.[29]
The evolutionaryhistoryof the species—whichdescribesthe characteristicsof the variousspecies
from which it descended—together with its genealogical relationship to every other species is
known as its phylogeny. Widely varied approaches to biology generate information about
phylogeny.These include the comparisons of DNA sequences conducted withinmolecular biology
or genomics,andcomparisonsof fossilsorotherrecordsof ancientorganisms inpaleontology.[30]
Biologists organize and analyze evolutionary relationships through various methods, including
phylogenetics,phenetics,andcladistics.(Fora summaryof major eventsinthe evolutionof life as
currently understood by biologists, see evolutionary timeline.)

Genetics
A Punnettsquare depictinga cross betweentwopeaplantsheterozygousforpurple (B) and white
(b) blossoms
Main article: Genetics
Genes are the primary units of inheritance in all organisms. A gene is a unit of heredity and
correspondstoaregionof DNA thatinfluencesthe formorfunctionof anorganisminspecificways.
All organisms,frombacteriato animals,share the same basicmachinerythatcopiesand translates
DNA into proteins. Cells transcribe a DNA gene into an RNA version of the gene, and a ribosome
thentranslatesthe RNA into a protein,a sequence of aminoacids. The translationcode from RNA
codonto aminoacid isthe same for mostorganisms,butslightlydifferentforsome.Forexample,a
sequence of DNA that codes for insulinin humans also codes for insulinwhen inserted into other
organisms, such as plants.[31]
DNA usuallyoccursaslinearchromosomesineukaryotes,andcircularchromosomesinprokaryotes.
A chromosome is an organizedstructure consistingof DNA and histones.The setof chromosomes
in a cell and any other hereditary information found in the mitochondria, chloroplasts, or other
locations is collectively known as its genome. In eukaryotes, genomic DNA is located in the cell
nucleus,alongwithsmallamountsinmitochondriaandchloroplasts.Inprokaryotes,the DNA isheld
withinanirregularlyshapedbodyinthe cytoplasmcalledthe nucleoid.[32] The geneticinformation
in a genome isheldwithingenes,andthe complete assemblage of this informationinanorganism
is called its genotype.[33]
Homeostasis
Main article: Homeostasis
The hypothalamus secretes CRH, which directs the pituitary glandto secrete ACTH. In turn, ACTH
directsthe adrenal cortex tosecrete glucocorticoids,suchas cortisol.The GCsthenreduce the rate
of secretionbythe hypothalamusandthe pituitaryglandonce asufficientamountof GCshasbeen
released.[34]
Homeostasisisthe abilityof anopensystemtoregulate itsinternalenvironmenttomaintainstable
conditions by means of multiple dynamic equilibrium adjustments controlled by interrelated
regulation mechanisms. All living organisms, whether unicellular or multicellular, exhibit
homeostasis.[35]

To maintaindynamicequilibriumandeffectivelycarry out certainfunctions,a systemmust detect
and respond to perturbations. After the detection of a perturbation,a biological system normally
responds through negative feedback. This means stabilizing conditions by either reducing or
increasing the activity of an organ or system. One example is the release of glucagon when sugar
levels are too low.
Basic overview of energy and human life.
Energy
The survival of alivingorganismdependsonthe continuousinputof energy.Chemicalreactionsthat
are responsible foritsstructure and functionare tunedto extractenergyfrom substancesthatact
as its foodand transformthemto helpformnew cellsand sustainthem.Inthisprocess,molecules
of chemical substances that constitute food play two roles; first, they contain energy that can be
transformedforbiological chemical reactions;second,theydevelopnew molecularstructuresmade
up of biomolecules.
The organismsresponsibleforthe introductionof energyintoanecosystemare knownasproducers
or autotrophs. Nearly all of these organisms originally draw energy from the sun.[36] Plants and
otherphototrophsuse solarenergyviaaprocessknownasphotosynthesistoconvertraw materials
into organic molecules, such as ATP, whose bonds can be broken to release energy.[37] A few
ecosystems, however, depend entirely on energy extracted by chemotrophs from methane,
sulfides, or other non-luminal energy sources.[38]
Some of the captured energy is used to produce biomass to sustain life and provide energy for
growthanddevelopment.The majorityof the restof thisenergyislostasheatandwaste molecules.
The mostimportantprocessesforconvertingthe energytrappedinchemical substancesintoenergy
useful to sustain life are metabolism[39] and cellular respiration.[40]
Study and research
Structural
Main articles: Molecular biology, Cell biology, Genetics and Developmental biology
Schematic of typical animal cell depicting the various organelles and structures.
Molecularbiologyisthe studyof biologyatamolecularlevel.[41] Thisfieldoverlapswithotherareas
of biology,particularlywithgeneticsandbiochemistry.Molecularbiologychieflyconcernsitselfwith

understandingtheinteractionsbetweenthe varioussystemsof acell,includingtheinterrelationship
of DNA, RNA, and protein synthesis and learning how these interactions are regulated.
Cell biology studies the structural and physiological properties of cells, including their behaviors,
interactions, and environment. This is done on both the microscopic and molecular levels, for
unicellularorganismssuchasbacteria,aswell asthe specializedcellsinmulticellularorganismssuch
as humans.Understandingthe structure andfunctionof cellsisfundamental toall of the biological
sciences. The similarities and differences between cell typesare particularlyrelevant to molecular
biology.
Anatomy considers the forms of macroscopic structures such as organs and organ systems.[42]
Geneticsisthe scienceof genes,heredity,andthe variationof organisms.[43][44] Genesencode the
informationnecessaryforsynthesizingproteins,whichinturnplaya central role in influencingthe
final phenotype of the organism. In modern research, genetics provides important tools in the
investigation of the function of a particular gene, or the analysis of genetic interactions.Within
organisms,geneticinformationgenerallyiscarriedinchromosomes,where itisrepresentedinthe
chemical structure of particular DNA molecules.
Developmental biology studies the process by which organisms grow and develop. Originating in
embryology, modern developmental biology studies the genetic control of cell growth,
differentiation,and "morphogenesis," which is the process that progressivelygives rise to tissues,
organs, and anatomy. Model organisms for developmental biology include the round worm
Caenorhabditiselegans,[45] the fruitflyDrosophilamelanogaster,[46] the zebrafishDaniorerio,[47]
the mouse Mus musculus,[48] and the weed Arabidopsis thaliana.[49][50] (A model organism is a
species that is extensively studied to understand particular biological phenomena, with the
expectation that discoveries made in that organism provide insight into the workings of other
organisms.)[51]
Physiological
Main article: Physiology
Physiology studies the mechanical, physical, and biochemical processes of living organisms by
attemptingtounderstandhowall of the structuresfunctionasa whole.The theme of "structure to
function" is central to biology. Physiological studies have traditionally been divided into plant
physiologyandanimal physiology,butsome principlesof physiologyare universal,nomatterwhat
particular organism is being studied. For example, what is learned about the physiology of yeast
cellscanalsoapplyto humancells.The fieldof animal physiologyextendsthe toolsandmethodsof

humanphysiologytonon-humanspecies.Plantphysiologyborrowstechniquesfrombothresearch
fields.
Physiology studies how for example nervous, immune, endocrine, respiratory, and circulatory
systems, function and interact. The study of these systems is shared with medically oriented
disciplines such as neurology and immunology.
Evolutionary
Evolutionary research is concerned withthe originand descent of species, as well as their change
over time, and includes scientists from many taxonomicallyoriented disciplines. For example, it
generallyinvolvesscientistswhohave special traininginparticularorganismssuchas mammalogy,
ornithology, botany, or herpetology, but use those organisms as systems to answer general
questions about evolution.
Evolutionary biology is partly based on paleontology, which uses the fossil record to answer
questions about the mode and tempo of evolution,[52] and partly on the developments in areas
such as population genetics.[53] In the 1980s, developmental biology re-entered evolutionary
biology from its initial exclusion from the modern synthesis through the study of evolutionary
developmental biology.[54] Related fields often considered part of evolutionary biology are
phylogenetics, systematics, and taxonomy.
Systematic
A phylogenetic tree of all living things, based on rRNA gene data, showing the separation of the
three domains bacteria, archaea, and eukaryotes as described initially by Carl Woese. Trees
constructedwithothergenesare generallysimilar,althoughtheymayplace some early-branching
groups very differently, presumably owing to rapid rRNA evolution.The exact relationships of the
three domains are still being debated.
The hierarchyof biologicalclassification'seightmajortaxonomicranks.Intermediateminorrankings
are not shown. This diagram uses a 3 Domains / 6 Kingdoms format
Main article: Systematics
Multiple speciation events create a tree structured system of relationships between species. The
role of systematicsistostudythese relationshipsandthusthe differencesandsimilaritiesbetween
speciesandgroupsof species.[55] However,systematicswasanactive fieldof researchlongbefore
evolutionary thinking was common.[56]

Traditionally,livingthings have beendivided into five kingdoms: Monera; Protista; Fungi; Plantae;
Animalia.[57] However, many scientists now consider this five-kingdom system outdated.Modern
alternative classificationsystemsgenerallybeginwiththe three-domainsystem:Archaea(originally
Archaebacteria);Bacteria(originallyEubacteria)andEukaryota(includingprotists,fungi,plants,and
animals)[58] These domains reflect whether the cells have nuclei or not, as well as differences in
the chemical composition of key biomolecules such as ribosomes.[58]
Further, each kingdom is broken down recursively until each species is separately classified. The
order is: Domain; Kingdom; Phylum; Class; Order; Family; Genus; Species.
Outside of these categories, there are obligate intracellular parasites that are "on the edge of
life"[59] in terms of metabolic activity, meaning that many scientists do not actually classify these
structures as alive, due to their lack of at least one or more of the fundamental functions or
characteristics that define life. They are classified as viruses, viroids, prions, or satellites.
The scientific name of an organism is generated from its genus and species. For example, humans
are listedasHomosapiens.Homoisthe genus,andsapiensthe species.Whenwritingthe scientific
name of an organism,itis properto capitalize the firstletterinthe genusandput all of the species
in lowercase.[60] Additionally, the entire term may be italicized or underlined.[61]
The dominantclassificationsystemiscalledthe Linnaeantaxonomy.Itincludesranksandbinomial
nomenclature. How organisms are named is governed by international agreements such as the
International Code of Nomenclature for algae, fungi, and plants (ICN), the International Code of
Zoological Nomenclature (ICZN), and the International Code of Nomenclature of Bacteria (ICNB).
The classification of viruses, viroids, prions, and all other sub-viral agents that demonstrate
biological characteristics is conducted by the International Committee on Taxonomy of Viruses
(ICTV) and is known as the International Code of Viral Classification and Nomenclature
(ICVCN).[62][63][64][65] However, several other viral classification systems do exist.
A mergingdraft,BioCode, waspublishedin1997inanattempttostandardize nomenclatureinthese
three areas,but has yetto be formallyadopted.[66] The BioCode drafthasreceivedlittle attention
since 1997; itsoriginallyplannedimplementationdate of January1, 2000, has passedunnoticed.A
revised BioCode that, instead of replacing the existing codes, would provide a unified context for
them, was proposed in 2011.[67][68][69] However, the International Botanical Congress of 2011
declinedtoconsiderthe BioCodeproposal.The ICVCNremainsoutsidethe BioCode,whichdoesnot
include viral classification.

Ecological and environmental
Mutual symbiosis between clownfish of the genus Amphiprion that dwell among the tentacles of
tropical seaanemones.The territorial fishprotectsthe anemone fromanemone-eatingfish,andin
turn the stinging tentacles of the anemone protects the clown fish from its predators.
Main articles: Ecology, Ethology, Behavior and Biogeography
Ecology studies the distribution and abundance of living organisms, and the interactions between
organisms and their environment.[70] The habitat of an organism can be described as the local
abiotic factors such as climate and ecology, in addition to the other organisms and biotic factors
that share its environment.[71] One reason that biological systems can be difficult to study is that
so many different interactions with other organisms and the environment are possible,even on
small scales. A microscopic bacteriumin a local sugar gradient is responding to its environment as
much as a lion searching for food in the African savanna. For any species, behaviors can be co-
operative, competitive, parasitic, or symbiotic. Matters become more complex when two or more
species interact in an ecosystem.
Ecological systems are studied at several different levels, from individuals and populations to
ecosystems and the biosphere. The term population biology is often used interchangeably with
population ecology, although population biologyis more frequentlyused when studying diseases,
viruses,andmicrobes,whilepopulationecologyismore commonlyusedwhenstudyingplantsand
animals. Ecology draws on many subdisciplines.
Ethology studies animal behavior (particularly that of social animals such as primates and canids),
andissometimesconsideredabranchof zoology.Ethologistshave beenparticularlyconcernedwith
the evolution of behavior and the understanding of behavior in terms of the theory of natural
selection.Inone sense,the firstmodernethologistwasCharlesDarwin,whose book,The Expression
of the Emotions in Man and Animals, influenced many ethologists to come.[72]
Biogeographystudiesthe spatialdistributionof organismsonthe Earth,focusingontopicslikeplate
tectonics, climate change, dispersal and migration, and cladistics.
Basic unresolved problems in biology
Main article: List of unsolved problems in biology
Despite the profound advances made over recent decades in our understanding of life's
fundamental processes, some basic problemshave remained unresolved. For example, one of the
major unresolved problems in biology is the primary adaptive function of sex, and particularly its
keyprocessesineukaryotes,meiosisandhomologousrecombination.One view isthatsex evolved

primarily as an adaptation for increasing genetic diversity (see references e.g.[73][74]). An
alternative view is that sex is an adaptation for promoting accurate DNA repair in germ-line DNA,
and that increased genetic diversity is primarily a byproduct that may be useful in the long
run.[75][76] (See also Evolution of sexual reproduction).
Another basic unresolved problem in biologyis the biologic basis of aging. At present, there is no
consensusviewonthe underlyingcause of aging.Variouscompetingtheoriesare outlinedin Ageing
Theories.

Biology

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